The present invention relates to a data transmission system for transmitting order-characters, address-characters and information-characters between a master unit and one or more remote groups of subordinated terminal units, the several units in a group normally being disposed at a common location such as a branch bank or store. Each of said groups and said master unit includes a modulator and a demodulator, i.e. a so-called "modem", adapting pulses from the master unit and the subordinated terminal units to the transmission characteristics of the transmission lines which connect said master unit and said subordinated terminal units to each other.
To interconnect an equipment built up of pulse circuits with another such equipment over a relatively long distance, it is necessary to convert the pulses into signals which are adapted to the frequency characteristics of the transmission lines. For this purpose, it is common practice to employ at one end of the line a modulator for converting a pulse into either a phase shifted or frequency shifted pulse relative to a reference signal, and to connect the other end of the line to a demodulator detecting this phase or frequency shift and producing a pulse in correspondence thereto.
In systems where a plurality of pulse equipments disposed at geographically remote places are to be connected to a master pulse equipment, it is common practice to connect these remote pulse equipments and their associated modulator/demodulator units in parallel to one single transmission line for the purpose of shortening the overall length of the transmission lines required. Further, it is common practice to concentrate all pulse equipments which have a common location to one single modulator/demodulator unit by means of a traffic concentrator which, in addition to its concentrating function, effects the control functions required for the above-mentioned parallel connection. This equipment, which effects the interconnection between a plurality of pulse equipments and one single modulator/demodulator unit and enables the connection of a plurality of such units of pulse equipments in parallel to one single transmission line, tends to become rather complicated.
A further disadvantage of connecting a plurality of such units in parallel to one single transmission line resides in that the most efficient mode of transmission, i.e. so called synchronous transmission, cannot be utilized, due to the fact that one demodulator will have to receive signals in alternating order from a plurality of modulators.
A further drawback of the above-mentioned parallel connection resides in that a great number of signals are required for maintaining the order of succession between the units connected to the line, and such sequence signals will intrude upon the time available for the transmission of information.